JP2005189147A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of highly accurate measurement by reducing a measurement error caused by resonant vibration of receiving ultrasonic vibrators. <P>SOLUTION: In this ultrasonic flowmeter, transmission/reception of an ultrasonic wave is performed, and the flow rate of a fluid moving along a passage is measured based on the propagation time difference between both directions of the ultrasonic wave. The flowmeter is equipped with a pair of ultrasonic vibrators 1, 2 functioning as a transmitter and a receiver of the ultrasonic wave respectively and arranged so as to form a propagation route of the ultrasonic wave in the fluid passage, a transmission part 51 for driving the transmitting ultrasonic vibrator functioning as the transmitter between the pair of ultrasonic vibrators, and a reception part 6 for adjusting the amplitude of a received signal by the ultrasonic wave received by the receiving ultrasonic vibrator functioning as the receiver between the pair of ultrasonic vibrators. The transmission part 51 drives the receiving ultrasonic vibrator at a different timing from the timing when the transmitting ultrasonic vibrator is driven for measuring the flow rate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid using ultrasonic waves and a flow measurement method using ultrasonic waves. The invention also relates to a gas meter.

  The ultrasonic flow meter has features such as a simple structure, a small number of mechanically movable parts, a wide range in which the flow rate can be measured, and no pressure loss due to the flow meter. In addition, recent advances in electronics technology have made it possible to improve the measurement accuracy of ultrasonic flowmeters. For this reason, research using an ultrasonic flowmeter has been made in various fields that require measurement of gas and liquid flow rates, including gas meters.

  Hereinafter, the structure and measurement principle of a conventional ultrasonic flowmeter will be described. FIG. 12 is a block diagram showing an example of a conventional ultrasonic flowmeter. The ultrasonic vibrators 1 and 2 are arranged so as to sandwich the flow path 12 through which the fluid flows. The ultrasonic transducers 1 and 2 function as a transmitter and a receiver, respectively. Specifically, when the ultrasonic transducer 1 is used as a transmitter, the ultrasonic transducer 2 is used as a receiver, and when the ultrasonic transducer 2 is used as a transmitter, the ultrasonic transducer 1 is a receiver. Used as As shown by a broken line in FIG. 13, the propagation path of the ultrasonic wave formed between the ultrasonic vibrators 1 and 2 is inclined by an angle θ with respect to the fluid flow direction.

  When the ultrasonic wave is propagated from the ultrasonic vibrator 1 to the ultrasonic vibrator 2, the ultrasonic wave advances in the forward direction with respect to the flow of the fluid, so that the speed is increased. On the other hand, when the ultrasonic wave is propagated from the ultrasonic vibrator 2 to the ultrasonic vibrator 1, the ultrasonic wave travels in the opposite direction with respect to the fluid flow, and therefore the speed is slow. Accordingly, the velocity of the fluid is obtained from the difference between the time for the ultrasonic wave to propagate from the ultrasonic vibrator 1 to the ultrasonic vibrator 2 and the time for the ultrasonic wave to propagate from the ultrasonic vibrator 2 to the ultrasonic vibrator 1. Can do. Further, the flow rate can be obtained from the product of the cross-sectional area of the flow path 12 and the flow velocity.

  As a specific method for obtaining the flow rate of the fluid in accordance with the above-described principle, a measurement method based on the single-around method will be specifically described.

  As shown in FIG. 12, the ultrasonic flowmeter includes a transmission unit 3 and a reception unit 6, and the ultrasonic transducer 1 is selectively connected to one of the transmission unit 3 or the reception unit 6 by the switching unit 10. At this time, the ultrasonic transducer 2 is connected to the other of the transmission unit 3 or the reception unit 6 to which the ultrasonic transducer 1 is not connected.

  When the transmission unit 3 and the ultrasonic transducer 1 are connected, the transmission unit 3 drives the ultrasonic transducer 1, and the generated ultrasonic wave reaches the ultrasonic transducer 2 across the flow of the fluid. The ultrasonic wave received by the ultrasonic transducer 2 is converted into an electric signal, and the received signal is amplified by the receiving unit 6. The level of the received signal is detected by the level detector 5.

  FIG. 14 shows an example of zero cross detection in a conventional ultrasonic flowmeter. The peak hold unit 13 generates a peak hold signal 15 from the received signal 14. The level detector 5 detects that the peak hold signal 15 has reached a predetermined level 16 and generates a detection signal 17. The zero cross detection unit 7 detects a zero cross point immediately after the detection signal 17 is generated, and generates a zero cross detection signal 18. The zero cross point is a point at which the amplitude value of the received signal changes from positive to negative or from negative to positive. This zero cross point is the time when the ultrasonic wave reaches the ultrasonic vibrator 2. The delay unit 4 generates a trigger signal at a timing when a predetermined time has elapsed after receiving the zero-cross detection signal 18. The repeater 8 determines whether or not to repeat the measurement by sing-around, and outputs a trigger signal to the transmitter 3 if it repeats. The time from the generation of the zero cross detection signal 38 to the generation of the trigger signal is called a delay time.

  The transmission unit 3 drives the ultrasonic transducer 1 based on the trigger signal to generate the next ultrasonic wave. Repeating the ultrasonic transmission-reception-signal detection-delay-transmission loop in this manner is called sing around, and the number of transmission / reception loops is called sing around.

  The time measuring unit 9 measures the time required to repeat the transmission / reception loop a predetermined number of times, and the measurement result is sent to the flow rate calculation unit 11. Next, the switching unit 10 is switched, and the ultrasonic transducer 2 is used as a transmitter and the ultrasonic transducer 1 is used as a receiver to perform the same measurement.

  A value obtained by subtracting a value obtained by multiplying the delay time and the number of sing-around times from the time measured by the above-described method, and further dividing the value by the number of sing-around times is the ultrasonic wave propagation time.

  The propagation time when the ultrasonic transducer 1 is on the transmission side is T1, and the propagation time when the ultrasonic transducer 2 is on the transmission side is T2. Further, as shown in FIG. 13, the distance between the ultrasonic transducer 1 and the ultrasonic transducer 2 is L, and the fluid flow velocity and the ultrasonic sound velocity are V and C, respectively. At this time, T1 and T2 are represented by the following formula (1).

これらの式から流速Ｖは以下の式（２）で表される。

From these equations, the flow velocity V is expressed by the following equation (2).

  If the flow velocity V of the fluid is obtained, the flow rate Q is obtained from the product of the cross-sectional area of the flow path 14 and the flow velocity V.

  In the ultrasonic flowmeter having such a structure, a two-way propagation time difference of ultrasonic waves between the ultrasonic transducer 1 and the ultrasonic transducer 2 is measured as a fluid flow velocity. For this reason, when there is a difference in characteristics between the two ultrasonic transducers, a measurement error occurs.

  One method for reducing the measurement error is to use two ultrasonic transducers having the same characteristics. It is not impossible to select two ultrasonic transducers having the same characteristics. However, it takes time and cost to select appropriate two ultrasonic transducers. For this reason, this method is not suitable for consumer-use ultrasonic flowmeters that are required to be mass-produced at low cost, such as household gas meters.

As another method for reducing the measurement error, Patent Document 1 and Patent Document 2 describe an output impedance and a reception unit of the transmission unit 3 including the switching unit 10 when viewed from the ultrasonic transducer 1 and the ultrasonic transducer 2 side. 6 to make the input impedances equal. According to this method, even if there is a characteristic difference between two ultrasonic transducers, there is a difference in received waves between when the new ultrasonic device 1 is a receiver and when the ultrasonic transducer 2 is a receiver. Can be prevented from occurring.
Patent No. 1978010 Japanese Patent No. 2777084

  However, according to the research by the present inventor, it has been found that even if the ultrasonic flowmeter is manufactured by making the impedances on the transmission circuit side and the reception circuit side equal, a measurement error still occurs. As a result of detailed examination, it has been found that this measurement error is caused by a drive signal for driving the transmitting ultrasonic transducer leaking to the receiving ultrasonic transducer.

  As shown in FIG. 15, in the ultrasonic flowmeter having the above-described structure, the switching unit 10 connects the transmission unit 3 and the reception unit 6 to the ultrasonic transducer 1 and the ultrasonic transducer 2. Since each of the ultrasonic transducer 1 and the ultrasonic transducer 2 needs to be connected to the transmission unit 3 and the reception unit 6 by the switching unit 10, the ultrasonic transducer 1 and the ultrasonic wave are switched in the switching unit 10. The wirings that are electrically connected to the vibrator 2 are arranged close to each other. For this reason, even if the transmission unit 3 is electrically connected to the ultrasonic transducer 1, the transmission unit 3 and the ultrasonic transducer 2 are electrically connected via the parasitic capacitance 42. ing. As a result, the drive signal St output from the transmission unit 3 is output to the ultrasonic transducer 1 by the switching unit 10 and also to the ultrasonic transducer 2 as a leakage signal St ′ that propagates through the parasitic capacitance 42. Is output.

  FIG. 16 shows the displacement due to the vibration of the ultrasonic transducer 1 and the ultrasonic transducer 2 when the drive signal St is output from the transmission unit 3. In the figure, the horizontal axis represents time. As shown in FIG. 16, when the ultrasonic transducer 1 vibrates due to the drive signal St, the ultrasonic transducer 2 also begins to vibrate due to the leakage signal St ′ propagating through the parasitic capacitance 42. That is, the reception-side ultrasonic transducer 2 starts to vibrate before receiving the ultrasonic wave propagating through the fluid to be measured.

  The ultrasonic transducer 1 vibrated by the drive signal St transmits ultrasonic waves to the fluid. On the other hand, in the ultrasonic transducer 2, the leakage signal St ′ is also attenuated as the drive signal St is attenuated, so that the vibration of the ultrasonic transducer 2 is also attenuated. However, the vibration does not stop completely, and the ultrasonic vibrator 2 continues to vibrate at the resonance frequency of the ultrasonic vibrator 2 itself. Thereafter, the ultrasonic transducer 1 receives the ultrasonic wave transmitted from the ultrasonic transducer 1 and propagated through the fluid, and the ultrasonic transducer 1 vibrates as a reception signal Sr. At this time, the resonance vibration generated due to the leakage signal St ′ and the reception signal Sr are superimposed, and the waveform of the reception signal Sr is deformed.

  FIG. 17 illustrates zero cross detection in this case. Since the resonance vibration component 25 generated due to the leakage signal St ′ is superimposed on the reception signal 14, the signal output from the ultrasonic transducer 2 to the reception unit 6 as the reception signal is the reception signal 14 ′. For this reason, the time 27 delayed from the true zero cross detection time 26 becomes the zero cross detection time.

  Such an error also occurs when the ultrasonic transducer 2 is used as a transmitter. Further, the resonance vibration component 25 is different for each characteristic of the ultrasonic vibrator. Accordingly, if the characteristics of the two ultrasonic transducers are not completely equal, a measurement error based on such a leakage signal occurs.

  According to the study of the present inventor, for example, when the ultrasonic flowmeter is used for a household gas meter, the amplitude of the resonance vibration component 25 caused by the leakage signal is − Even 68 dB (about 4 / 10,000) causes a measurement error of 0.4 L / h at the maximum. Household gas meters are also required to have a function of detecting gas leaks. Since gas leaks are discriminated based on a flow rate of about 1 L / h, the measurement error due to the leak signal has an effect on gas leak detection. A sufficiently large value.

  An object of the present invention is to solve such problems of the prior art and to provide an ultrasonic flowmeter with a small measurement error.

  The ultrasonic flowmeter of the present invention transmits and receives ultrasonic waves, and measures the flow rate at which the fluid moves in the flow path based on the two-way propagation time difference of the ultrasonic waves. Each of the ultrasonic flowmeters functions as an ultrasonic transmitter and receiver, and a pair of ultrasonic transducers arranged so as to form the ultrasonic wave propagation path in a fluid flow path, and the pair of ultrasonic flowmeters A transmitting unit that drives a transmitting ultrasonic transducer that functions as the transmitter, and a receiving ultrasonic vibration that functions as the receiver of the pair of ultrasonic transducers A reception unit that adjusts the amplitude of the reception signal by the ultrasonic wave received by the child, and the transmission unit is configured to receive the reception signal at a timing different from a timing at which the transmission ultrasonic transducer is driven to measure a flow rate. Drive the ultrasonic transducer.

  In a preferred embodiment, the transmission unit drives the reception ultrasonic transducer so as to reduce the influence of resonance vibration of the reception ultrasonic transducer.

  In a preferred embodiment, the propagation time of the ultrasonic wave in one direction is obtained by transmitting the ultrasonic wave a plurality of times at different timings for driving the reception ultrasonic transducer.

  The ultrasonic flowmeter of the present invention is a pair of ultrasonic vibrations that function as an ultrasonic transmitter and a receiver, respectively, and are arranged so as to form the ultrasonic wave propagation path in the fluid flow path. A first drive signal for driving a transmitting ultrasonic transducer functioning as the transmitter among the pair of ultrasonic transducers at a first timing and the pair of ultrasonic transducers of the pair of ultrasonic transducers A transmission unit that outputs a second drive signal for driving a reception ultrasonic transducer functioning as a receiver at a second timing, and an amplitude of a reception signal by the ultrasonic wave received by the reception ultrasonic transducer The transmission unit is connected to one of the pair of ultrasonic transducers so that ultrasonic waves are transmitted and received bidirectionally between the reception unit for adjusting the frequency and the pair of ultrasonic transducers, and the pair of ultrasonic vibrations Connect the receiver to the other child And a detection unit that detects the received signal, and based on the detection of the received signal, obtains a propagation time for the ultrasonic wave to propagate through a propagation path, and determines the flow rate of the fluid from the propagation time difference in both directions. Ask.

  In a preferred embodiment, the ultrasonic flowmeter has a detection signal indicating that a reception signal has been detected from the detection unit in order to measure the flow rate of the fluid by repeatedly transmitting and receiving the ultrasonic wave by a single-around method. And a controller that outputs a trigger signal for outputting the first and second drive signals to the transmitter after receiving a predetermined time.

  In a preferred embodiment, in the repetition by the sing-around method, the first timing is constant and the second timing is changed.

  In a preferred embodiment, the second timing is determined based on a resonance frequency of the ultrasonic transducer.

  In a preferred embodiment, the second timing is periodically changed in the repetition by the sing-around method.

  In a preferred embodiment, the number of repetitions by the sing-around method is an integral multiple of the number of occurrences of the periodic change of the second timing.

  In a preferred embodiment, the second timing is determined so that the second drive signal is output before the reception ultrasonic transducer receives the ultrasonic wave transmitted by the first drive signal. It has been.

  In a preferred embodiment, the driving of the receiving ultrasonic transducer by the transmitting unit is performed by the second driving signal being generated by a high impedance connection between the receiving ultrasonic transducer and the transmitting unit in the switching unit. This is performed by being output from the transmitter to the ultrasonic transducer for reception.

  In a preferred embodiment, the transmission unit receives the trigger signal and generates the first drive signal, and receives the trigger signal and outputs a signal after a predetermined time has elapsed. A delay unit; a second waveform generation unit that receives the signal from the delay unit and generates the second drive signal; and a signal amplifier that amplifies the first drive signal and the second drive signal Part.

  In a preferred embodiment, the driving of the reception ultrasonic transducer by the transmission unit is performed by the low-frequency connection between the receiver ultrasonic transducer and the transmission unit in the switching unit. This is performed by being output from the transmitter to the ultrasonic transducer for reception.

In a preferred embodiment, the transmission unit is inserted between the control unit and the switching unit, receives the trigger signal and generates the first drive signal, and the first drive signal generation unit, A delay unit that receives the trigger signal and outputs the signal after a predetermined time;
From the second drive signal generation unit that receives the signal from the delay unit, generates the second drive signal, and outputs the second drive signal to the switching unit, and from the second drive signal generation unit While the second drive signal is generated, the switch unit includes a switch unit that cuts off an electrical connection between the switching unit and the receiving unit.

  The gas meter of the present invention includes the ultrasonic flow meter defined in any of the above.

  In the ultrasonic flowmeter method of the present invention, a pair of ultrasonic transducers each functioning as an ultrasonic transmitter and a receiver are arranged so that an ultrasonic propagation path is formed in the fluid flow path. The flow rate of the fluid is measured based on the two-way propagation time difference of the ultrasonic wave propagating through the propagation path, and the transmitting ultrasonic transducer that uses the receiving ultrasonic transducer functioning as a receiver as the transmitter is driven. It is driven at a timing different from the timing to perform.

  In a preferred embodiment, the reception ultrasonic transducer is driven so as to reduce the influence of resonance vibration of the reception ultrasonic transducer.

  In a preferred embodiment, the propagation time of the ultrasonic wave in one direction is obtained by transmitting the ultrasonic wave a plurality of times at different timings for driving the reception ultrasonic transducer.

  In a preferred embodiment, the ultrasonic wave propagation time is obtained from the total time required for repetition by repeating the transmission / reception of the ultrasonic wave by a single-around method.

  In a preferred embodiment, the method includes a first drive signal for driving the transmission ultrasonic transducer at a first timing and a second drive for driving the reception ultrasonic transducer at a second timing. A step of outputting a signal, wherein the first timing is made constant and the second timing is changed in the repetition by the sing-around method.

  In a preferred embodiment, the second timing is determined based on a resonance frequency of the ultrasonic transducer.

  In a preferred embodiment, the second timing is periodically changed in repetition by the sing-around method.

  In a preferred embodiment, the number of repetitions by the sing-around method is set to an integral multiple of the number of times that the second timing is periodically changed.

  In a preferred embodiment, the second timing is determined so that the second signal is output before the reception ultrasonic transducer receives the ultrasonic wave transmitted by the first signal.

  In a preferred embodiment, the reception ultrasonic transducer includes the pair of ultrasonic transducers, a transmission unit that generates the first and second drive signals, and reception received by the reception ultrasonic transducer. A switching unit for selectively connecting a receiving unit that adjusts the amplitude of the signal, and the second signal is generated by a high impedance connection between the ultrasonic transducer for reception and the transmitting unit in the switching unit. Is output from the transmitter to the ultrasonic transducer for reception.

  In a preferred embodiment, the reception ultrasonic transducer includes the pair of ultrasonic transducers, a transmission unit that generates the first and second drive signals, and reception received by the reception ultrasonic transducer. A switching unit for selectively connecting a receiving unit that adjusts the amplitude of the signal, and the second signal is generated by a low impedance connection between the ultrasonic transducer for reception and the transmitting unit in the switching unit. Is output from the transmitter to the ultrasonic transducer for receiver.

  The computer-readable recording medium of the present invention records a program for causing a computer to execute the flow rate measuring method defined in any of the above.

  According to the present invention, the reception ultrasonic transducer is driven at a timing different from the timing at which the transmission ultrasonic transducer is driven in order to measure the flow rate. For this reason, it becomes possible to adjust the phase of the resonance vibration of the ultrasonic transducer for reception with respect to the phase of vibration generated by receiving the ultrasonic wave propagating through the fluid. Therefore, the influence of the resonance vibration can be reduced by differentiating the phase of the resonance vibration and receiving a plurality of times, thereby realizing an ultrasonic flowmeter and an ultrasonic flow measurement method with a small measurement error.

(First embodiment)
FIG. 1 is a block diagram showing a first embodiment of an ultrasonic flowmeter according to the present invention. The ultrasonic flowmeter 101 includes a first ultrasonic transducer 1 and a second ultrasonic transducer 2 that are arranged so as to form an ultrasonic propagation path in the fluid flow path 12, a transmission unit 51, and the like. The receiving unit 6 is provided.

  The first ultrasonic transducer 1 and the second ultrasonic transducer 2 function as a transmitter and a receiver, respectively. The ultrasonic wave transmitted from the first ultrasonic transducer 1 is received by the second ultrasonic transducer 2, and the ultrasonic wave transmitted from the second ultrasonic transducer 2 is the first ultrasonic transducer 1. Receive by. These bidirectional propagation paths form an angle θ with respect to the flow direction of the fluid flowing through the flow path 12. The magnitude of the angle θ is selected from the range of 10 to 40 degrees. Hereinafter, an ultrasonic transducer used as a receiver is referred to as a receiving ultrasonic transducer, and a transmitting ultrasonic transducer is referred to as a transmitting ultrasonic transducer. As described above, according to the propagation direction of the ultrasonic wave, each of the first ultrasonic vibrator 1 and the second ultrasonic vibrator 2 becomes a receiving ultrasonic vibrator, Become.

  The first ultrasonic transducer 1 and the second ultrasonic transducer 2 are driven at a frequency of approximately 20 kHz or more according to vibration modes such as a thickness vibration mode, a side-slip vibration mode, and a longitudinal vibration mode. As such, various conventionally used ultrasonic transducers can be used. The optimum frequency is appropriately selected according to the state and type of the fluid to be measured and the predicted flow velocity. In the present embodiment, for example, an ultrasonic vibrator that vibrates in a thickness vibration mode and has a resonance frequency of 500 kHz is used.

  The first ultrasonic transducer 1 and the second ultrasonic transducer 2 are connected to the transmission unit 51 and the reception unit 6 via the switching unit 10. The switching unit 10 may be a mechanical device such as a toggle switch, or may be configured by an electronic unit or the like. When the transmission unit 51 and the first ultrasonic transducer 1 are electrically connected with low impedance, the second ultrasonic transducer 2 is electrically connected with the reception unit 6 with low impedance (for example, 30Ω). The At this time, the transmission unit 51 and the second ultrasonic transducer 2, and the reception unit 6 and the first ultrasonic transducer 1, which are combinations that are not selected, have the capacity as described with reference to FIG. They are connected with high impedance (for example, 10 kΩ) by coupling. That is, the transmission unit 51 and the second ultrasonic transducer 2, and the reception unit 6 and the first ultrasonic transducer 1 are the transmission unit 51 and the first ultrasonic transducer 1, and the reception unit 6 and The second ultrasonic transducer 2 is electrically connected with an impedance much higher than that of the second ultrasonic transducer 2.

  Further, when the transmission unit 51 and the second ultrasonic transducer 2, and the reception unit 6 and the first ultrasonic transducer 1 are electrically connected with low impedance, the transmission unit 51 and the first ultrasonic transducer are connected. The vibrator 1, the receiving unit 6, and the second ultrasonic vibrator 2 are electrically connected with high impedance.

  As will be described in detail below, the transmission unit 51 includes a first drive signal for transmitting measurement ultrasonic waves from the transmission ultrasonic transducer and a first drive signal for driving the reception ultrasonic transducer. 2 drive signals are generated. Usually, a receiving ultrasonic transducer receives an ultrasonic wave and outputs an electrical signal. In the present invention, ultrasonic waves are received in a state where the ultrasonic transducer for reception is actively driven and vibrated. The reception ultrasonic transducer is driven by high impedance connection between the transmission unit 51 and the reception ultrasonic transducer in the switching unit 10 described above. The first drive signal for driving the transmission ultrasonic transducer also leaks to the reception ultrasonic transducer through a high impedance connection and vibrates in the same manner as in the prior art. However, in the present invention, after the first drive signal, The receiving ultrasonic transducer is driven using a second drive signal generated at a timing different from that of the drive signal. This reduces the influence of resonance vibration of the receiving ultrasonic transducer.

  Specifically, the transmission unit 51 includes a first waveform generation unit 20, a second waveform generation unit 21, a delay unit 22, and an amplification unit 52. The delay unit 22 and the second waveform unit 21 are connected in series and connected in parallel to the first waveform generation 20. These parallel circuits are inserted between the amplification unit 52 and the control unit 54.

When the trigger signal is output from the control unit 54, the first waveform generation unit 20 receives the trigger signal, generates a first drive signal at a predetermined first timing, and outputs the first drive signal to the amplification unit 52.
Further, when the delay unit 22 receives the trigger signal, the delay unit 22 outputs the signal to the second waveform generation unit 21 at a second timing after a predetermined delay time has elapsed. The second waveform generator 21 receives the signal and outputs a second drive signal. That is, the second drive signal is generated at the second timing. The generated second drive signal is output to the amplifying unit 52.

  When the first ultrasonic transducer 1 is used for transmission, the switching unit 10 connects the transmission unit 51 and the first ultrasonic transducer 1 with low impedance. The first drive signal and the second drive signal generated by the transmission unit 51 drive the first ultrasonic transducer 1, and ultrasonic waves are transmitted into the fluid. At this time, the second ultrasonic transducer 2 connected in high impedance with the transmitter 51 is driven by the first drive signal and the second drive signal attenuated by the high impedance.

  Thereafter, the ultrasonic wave that reaches the second ultrasonic transducer 2 is converted into an electric signal, and the amplitude of the received signal is adjusted by the receiving unit 6. Usually, since the output of the receiving ultrasonic transducer is small, the received signal is amplified with an appropriate amplification factor. However, when the electrical signal generated by the ultrasonic wave that reaches the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is sufficiently large, the receiving unit 6 does not necessarily amplify the received signal.

  The ultrasonic flowmeter 101 further includes a detection unit 53, a control unit 54, and a calculation unit 55. The reception signal amplified by the reception unit 6 is sent to the detection unit 53. The detection unit 53 detects the reception signal and determines the time when the reception signal is received. The detection unit 53 includes a zero cross detection unit 7, a peak hold unit 13, and a level detection unit 5. As described with reference to FIG. 14, the peak hold unit 13 receives the reception signal 14 and generates the peak hold signal 15 that holds the peak value of the reception signal 14. The level detector 5 outputs a signal 17 to the zero cross detector 7 when the peak hold signal 15 reaches a predetermined threshold value 16. The zero cross detection unit 7 detects a point where the amplitude of the reception signal 14 changes from positive to negative or from negative to positive immediately after receiving the signal from the level detection unit 5, and generates a detection signal 18. . This zero cross point is defined as the propagation time of the received signal.

  The control unit 54 receives the detection signal 18 and outputs a trigger signal to the transmission unit after a predetermined delay time has elapsed. For this purpose, the control unit 54 includes a delay unit 4 and a repetition unit 8. The delay unit 4 generates a trigger signal at a timing delayed by a predetermined time based on the detection signal. The repetition unit 8 counts the trigger signal of the delay unit 4, and outputs the output of the delay unit 4 to the transmission unit 51 if it is equal to or less than a predetermined number. The transmission unit 51 receives the trigger signal and generates the next first drive signal and second drive signal as described above. In this way, transmission / reception of ultrasonic waves is repeated by the sing-around method.

  The calculation unit 54 includes a timer unit 9 and a flow rate calculation unit 11. The timer 9 measures the time required to repeat the above transmission / reception loop a predetermined number of times, and sends the measurement result to the flow rate calculation unit 11. The flow rate calculation unit 11 transmits the ultrasonic wave from the first ultrasonic transducer 1 toward the second ultrasonic transducer 2 and the propagation time when the ultrasonic wave is propagated from the second ultrasonic transducer 2 to the first ultrasonic transducer 2. The propagation times when ultrasonic waves are propagated toward the sonic transducer 1 are obtained, and the flow velocity and flow rate are obtained from the propagation time difference.

  In the present embodiment, each of the above-described components can be configured by hardware using electronic components or the like, or can be configured by software. The flow rate calculation unit 11 is realized by a microcomputer or the like. This microcomputer also controls each component. When the function of each component described above is realized by software, each component means a procedure or process for realizing the function. In this case, each component may be called by replacing “part” with “step” such as “peak hold step” and “zero detection step”. In addition, the function can be realized by either hardware or software, and as long as the function of each component can be realized, there is no restriction on the configuration that realizes the function. Each component may be called by replacing “unit” with “means” such as “zero detection means”. In the following embodiments, each component can be similarly configured, and each component can be referred to.

  Next, signals received by the ultrasonic transducer for reception in the ultrasonic flowmeter 101 will be described. FIG. 2 shows the amplitude of the signal output from the transmitter 51, the vibration of the transmitting ultrasonic transducer, and the vibration of the receiving ultrasonic transducer. In the figure, the horizontal axis indicates time, which is based on the same time. As described above, the transmitter 51 outputs the first drive signal 61 and the second drive signal 62 when transmitting ultrasonic waves and measuring (detecting) the propagation time once. The first drive signal 61 is used to drive the transmission ultrasonic transducer, and the second drive signal 62 is used to drive the reception ultrasonic transducer. As shown in FIG. 2, when the first drive signal is output at time t1, the transmission ultrasonic transducer starts to vibrate with the waveform 61a at approximately the same time due to the first drive signal. At the same time, the first drive signal is also output to the receiving ultrasonic transducer by capacitive coupling in the switching unit. Therefore, the receiving ultrasonic transducer starts to vibrate with the waveform 61b. The amplitude of the waveform 61b is not as large as the waveform 61a. This is because the driving of the reception ultrasonic transducer is based on capacitive coupling, and thus the first drive signal is attenuated.

  When the output of the first drive signal 61 is completed, the vibrations of the transmission ultrasonic transducer and the reception ultrasonic transducer are attenuated. However, these ultrasonic vibrators continue to vibrate at the resonance frequency of each ultrasonic vibrator. For this reason, the receiving ultrasonic transducer continues to vibrate with the waveform 63. Similarly, the transmitting ultrasonic vibrator continues to vibrate at the resonance frequency. However, in the present invention, the vibration on the transmitter side is not important and is not shown in FIG.

  When the second drive signal 62 is output from the transmission unit 51 at time t2, similarly, the transmission ultrasonic transducer starts to vibrate with the waveform 62a at approximately the same time by the second drive signal. At the same time, the receiving ultrasonic transducer starts to vibrate with the waveform 62b. Thereafter, when the output of the second drive signal 62 is completed, the vibrations of the transmission ultrasonic transducer and the reception ultrasonic transducer are attenuated. Similarly, the reception ultrasonic transducer vibrates at the resonance frequency indicated by the waveform 64. Continue. At this time, the phase of the resonance vibration indicated by the waveform 64 is determined at the output time t2 of the second drive signal 62.

  Thereafter, the ultrasonic wave generated when the transmitting ultrasonic vibrator vibrates as indicated by the waveform 61a propagates in the fluid and reaches the receiving ultrasonic vibrator. At this time, the receiving ultrasonic transducer vibrating at the resonance frequency indicated by the waveform 64 vibrates as indicated by the waveform 61c by the received ultrasonic wave. That is, the vibration due to reception is superimposed on the resonance vibration. As shown in the figure, the time when the receiving ultrasonic transducer starts to vibrate by the ultrasonic wave propagating in the fluid is after the time t3 from the time t1, and this time is the propagation time for the ultrasonic wave to propagate in the fluid. be equivalent to. The time required for measuring several tens of times during measurement repeatedly performed by the sing-around method is sufficiently short, and there is almost no fluid flow rate change in such a short time. That is, t3 is constant during measurement by the sing-around method. The phase of the received ultrasonic wave is determined at the timing (time t1) at which the first drive signal is generated. On the other hand, the phase when the receiving ultrasonic transducer performs the resonant vibration indicated by the waveform 64 is determined at the timing (time t2) when the second drive signal is generated. For this reason, the phase of these two vibrations can be adjusted arbitrarily.

  By superimposing the reception signal on the resonance vibration, the zero cross point of the reception signal is also affected by the resonance vibration. In particular, when the resonance frequencies of the two ultrasonic transducers are different, the influence varies depending on the propagation direction of the ultrasonic waves. However, by determining the timing for generating the second drive signal based on the resonance frequency, it is possible to adjust the influence of the resonance vibration. Specifically, when obtaining the propagation time of the ultrasonic wave in one direction, the ultrasonic wave is transmitted and received a plurality of times with different resonance vibration phases. Thereby, the influence of the resonance vibration can be canceled. For example, the influence of resonance vibration can be canceled by periodically changing the vibration phase in repetition by the sing-around method.

  Hereinafter, a method for canceling the influence of resonance vibration when measuring the flow rate using the sing-around method will be described. Here, the resonance frequency of the ultrasonic transducer for reception is set to 500 kHz (period 2 μs). FIG. 3 shows the waveform of the drive signal output from the transmission unit 51. First, in the first measurement (repetition) among the repetitions of the measurement by the sing-around method, the first drive signal 28 is generated, for example, at the timing when the trigger signal is received from the control unit. Further, the second drive signal 29 is generated at a timing when a delay time 30 has elapsed since the generation of the first drive signal 28. The delay time 30 is created and adjusted by the delay unit 22 of the transmission unit 51. In the second measurement, as shown in the figure, the first drive signal 28 and the second drive signal 30 are generated. The generation timing of the first drive signal 28 is the same as the first measurement. On the other hand, the generation of the second drive signal 30 is delayed by the time d1 from the generation timing of the first drive signal 28. d1 is set to 0.2 μs, which is 1/10 of the period of resonance vibration of the receiving ultrasonic transducer.

  Thereafter, the generation timing of the first drive signal does not change for each measurement and is constant, but the generation timing of the second drive signal is delayed by 1/10 period. Therefore, in the tenth measurement, the generation timing of the first drive signal 28 coincides with the generation timing of the first drive signal 28 in the first time, but the generation timing of the second drive signal 31. Is delayed by a time d9, which is a 9/10 period (1.8 μs), from the generation timing of the second drive signal 29 at the first time. In the eleventh measurement, the generation timing of the second drive signal 29 is shifted by exactly one cycle from the second drive signal 29 in the first measurement, so that the second drive signal 29 in the first measurement is different from the second drive signal 29 in the first measurement. At the same timing.

  FIG. 4 shows a waveform of a signal that leaks to the receiving ultrasonic transducer via the switching unit 10 when the drive signal shown in FIG. 3 is output from the transmission unit 51. Since signal leakage occurs due to capacitive coupling, the waveforms of the drive signals are different. Further, in FIG. 4, the signal is shown with an amplitude substantially equal to that of the drive signal shown in FIG. 3 for easy viewing, but the actual amplitude is smaller than the amplitude of the drive signal generated by the transmission unit 51. .

  As shown in the figure, the timing of the leaked first drive signal 28r substantially coincides with the generation timing of the first drive signal in the transmission unit. That is, the timing of the leaked first drive signal 28r is constant during repetition by sing-around.

  The timing of the leaked second drive signal also substantially coincides with the timing at which the transmitter 51 generates the second drive signal. For this reason, the generation timing of the leaked second drive signal 30r in the second measurement and the leaked second drive signal 31r in the tenth measurement is the same as the generation timing of the leaked second drive signal in the first measurement. It is delayed by the time d1 (1/10 cycle) and d9 (9/10 cycle) from the generation timing of 29r. The generation timing of the leaked second drive signal 29r in the eleventh measurement is the same as in the first measurement.

  FIG. 5 shows a vibration waveform of the receiving ultrasonic transducer driven by the signal shown in FIG. The receiving ultrasonic transducer is driven and vibrated by the leaked first drive signal 28r and the leaked second drive signals 29r, 30r, 31r. As shown in the figure, the timing of the vibration waveform 28b generated by the leaked first drive signal 28r is constant during repetition of sing-around. In any of the repeated measurements by the sing-around method, when the output of the leaked first drive signal 28r is completed, the receiving ultrasonic transducer vibrates at the resonance frequency as shown by the waveform 65b.

  The timing of vibration of the receiving ultrasonic transducer driven by the leaked second drive signal also substantially coincides with the timing at which the transmitter 51 generates the second drive signal. Specifically, the timing of the vibration waveforms 30b and 31b generated by the leaked second drive signal 30r in the second measurement and the leaked second drive signal 31r in the tenth measurement is the first measurement. Is delayed by timing times d1 (1/10 cycle) and d9 (9/10 cycle) of the vibration waveform 29b generated by the leaked second drive signal 29r. That is, for each measurement by sing-around, the timing of vibration due to the leaked second drive signal is delayed by 1/10 period.

  Therefore, the vibration due to the leaked second drive signal is attenuated, and the phase of the vibration waveforms 66b, 67b, 68b when the receiving ultrasonic vibrator vibrates at the resonance frequency is 1 / Delayed by 10 cycles. Specifically, the phases of the vibration waveform 67b in the second measurement and the vibration waveform 68b in the tenth measurement are delayed by time d1 and d9 with respect to the vibration waveform 66b in the first measurement.

  FIG. 6 shows that the ultrasonic wave transmitted from the ultrasonic transducer for transmission by the first drive signal 28 propagates in the fluid in the state where the ultrasonic transducer for reception vibrates as shown in FIG. The vibration of the ultrasonic transducer when received by the reception ultrasonic transducer is shown. As shown in FIG. 6, the vibration waveform 28a is generated by receiving the ultrasonic wave. As described with reference to FIG. 2, since the time required to repeat the measurement by sing-around 10 times is short, the flow velocity does not change during this time, and the propagation time t3 of the ultrasonic wave propagating the fluid can be regarded as constant. For this reason, the timing at which the vibration waveform 28a occurs also coincides in any repetition due to sing-around.

  When the vibration waveform 28a is generated, the receiving ultrasonic transducer vibrates at the resonance frequency. As shown in the figure, in the first, second, tenth and eleventh measurements, the vibration waveforms 66b, 67b, 68b and 66b vibrate, and the vibration waveform 28a is superimposed on these vibration waveforms. At this time, the phase of the resonance vibration is delayed by 1/10 period for each measurement, and in the eleventh measurement, the phase coincides with the phase at the first measurement.

  The vibration waveform obtained by superimposing the vibration waveform of the received ultrasonic wave and the vibration waveform of the resonance vibration becomes the actual vibration waveform of the reception ultrasonic transducer, and corresponds to the reception signal output by the reception ultrasonic transducer. For this reason, the waveform of the received signal changes due to the influence of resonance vibration, and the zero cross point also varies from the true position. However, the resonance vibration of the receiving ultrasonic transducer can be approximated by a trigonometric function. When the measurement times from the first to the tenth times are summed up by sing around, the phase of the resonance vibration whose phase is shifted by 1/10 period The influence is summed for one period of the resonance vibration. For this reason, the influence of the resonance vibration is canceled by summing the measurement times from the first time to the tenth time, and the influence of the resonance frequency is eliminated in the obtained measurement time. In this case, the same effect can be obtained even if the number of times of single-around is an integer multiple of 10.

  FIG. 7A is a graph for explaining that the influence of resonance vibrations having different phases is canceled. In the figure, a waveform 33 shows a signal oscillating at a frequency of 500 kHz and a period of 2 μs. When one phase is generated by shifting the phase of this signal by 0.2 μs and superimposed on the generated nine signal waveforms 33, the signal shown in the waveform 34 is obtained. As can be seen from the figure, the amplitude of the signal is almost completely cancelled. From this, the influence by the resonance frequency can be canceled by performing measurement by sing-around as described above.

  FIG. 7B shows a waveform 35 of a signal oscillating at a frequency of 510 kHz and a period of 1.96 μs. When the period of this signal is divided into 10 equal parts, 0.96 μs is obtained. As in FIG. 7A, nine signals with phases delayed by 0.2 μs are generated and superimposed on the waveform 35 to obtain a waveform 36. The signal shown is obtained. As shown in the figure, the maximum amplitude of the waveform 36 is about 20% of the waveform 35. From this, it can be seen that even if the phase is shifted with reference to a frequency different from the resonance frequency by about 10 Hz and the measurement is repeated by sing around, the influence of the resonance vibration can be considerably reduced.

  In general, when the resonance frequency of the receiving ultrasonic transducer is f and N is an integer of 2 or more, the timing for generating the second drive signal is 1 / (fN) for each repeated measurement by sing-around. Change the phase step by step. Then, the number of sing-arounds may be set to an integer multiple of N (1 or more). Thereby, it is possible to prevent the influence of the resonance frequency from occurring in the measurement of the propagation time of the ultrasonic wave.

  The value of N is preferably 16 to 512. If it is smaller than 16, the number of measurement points to be measured in one period of the resonance vibration is reduced, and there is a possibility that the influence of the resonance vibration is not sufficiently canceled when the measurement time is totaled. On the other hand, when it is larger than 512, the measuring time of the sing-around required for totaling one period of the resonance vibration becomes longer. Thereby, depending on the flow velocity of the fluid to be measured, the flow velocity may not be considered constant during that time, and a measurement error may occur.

  In order to obtain such an effect and correctly measure the flow rate, as is apparent from FIG. 6, the second drive is performed before the receiving ultrasonic transducer receives the ultrasonic wave propagating in the fluid. It is necessary that a signal is output, and it is more preferable that the vibration waveform 29b based on the second drive signal is sufficiently attenuated and the ultrasonic transducer for reception vibrates at the resonance frequency.

  Although not shown in the figure, since the second drive signal also drives the transmission ultrasonic transducer, the ultrasonic wave transmitted from the transmission ultrasonic transducer by the second drive signal is used as the reception ultrasonic wave. A detection prohibition time may be provided so that the zero cross detection is not performed for a predetermined time after the ultrasonic wave generated by the first drive signal is detected by the detection unit 54 so that the transducer receives and is not detected by the detection unit 54. preferable.

  In the measurement of the flow rate, as shown in FIG. 1, it is necessary to measure the bidirectional propagation time between the first ultrasonic transducer 1 and the second ultrasonic transducer 2. Therefore, the resonance frequency f of the reception ultrasonic transducer is the first ultrasonic transducer 1 or the second ultrasonic transducer that is the reception ultrasonic transducer when the measurement is performed. It is preferable to use a resonance frequency f of 2. However, as described with reference to FIG. 7, even if the phase to be delayed is slightly different from the resonance frequency, the influence of resonance vibration can be reduced. Therefore, the resonance frequencies of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 do not match, but if the difference is about 10%, either one of these resonance frequencies, or these two The bidirectional propagation time may be measured using the average value of the resonance frequency of the ultrasonic transducer.

  Next, a procedure for measuring the flow rate of the fluid using the ultrasonic flowmeter 101 will be described. The procedure described below is performed by sequentially controlling each component by a computer such as a microcomputer, and a program for causing the computer to execute the procedure is an information recording medium such as a ROM, a RAM, a hard disk, or a magnetic recording medium. Is saved.

  First, as shown in FIG. 1, switching is performed so that the transmission unit 51 is connected to the first ultrasonic transducer 1 with low impedance, and the reception unit 6 is connected to the second ultrasonic transducer 2 with low impedance. The part 10 is switched.

  As illustrated in FIG. 8, the trigger signal 45 is input to the transmission unit 51. The first drive signal 28 (FIG. 3) is generated based on the trigger signal, and the second drive signal 29 is generated by the delay unit 22 after the delay time 30 has elapsed. The amplifier 3 amplifies them and generates ultrasonic waves from the first ultrasonic transducer 1 by the first drive signal and the second drive signal. At this time, the second ultrasonic transducer 2 is also driven by the first drive signal and the second drive signal leaking to the second ultrasonic transducer 2.

  The ultrasonic wave propagated through the flow path 12 is received by the second ultrasonic transducer 2. Since the second ultrasonic vibrator 2 is resonantly oscillated at the time of reception, a resonance vibration component oscillating at a predetermined phase by the second drive signal generated at a predetermined timing is superimposed on the received signal. doing. The reception signal 14 is amplified by the reception unit 6.

  In the detection unit 53, the received signal 14 is zero-cross detected, and the first measurement is completed. The controller 54 outputs the next trigger signal 47 to the transmitter 51 after a predetermined delay time 46 has elapsed since the zero cross detection. At this time, the number of trigger signals is counted. This constitutes a single loop of single-around.

  The transmitter 51 that has received the next trigger signal similarly generates the first and second drive signals for the second measurement. The timing for generating the first drive signal is the same as the timing for the first measurement, but the second drive signal is 1 / (fN from the timing for the first measurement by the delay unit 22. ) Delay. For example, when the resonance frequency is 500 kHz and N is 10, it is 0.2 μs.

  Similarly, the measurement is repeated by sing-around while delaying the time for generating the second drive signal by 0.2 μs. In the eleventh measurement, the delay time for generating the second drive signal uses the same value as in the first measurement.

  After repeating the transmission / reception loop for a predetermined number of times (for example, 50 to 1000 times) that is an integer multiple of N, the timer 9 measures and measures the total time 48 required to repeat the loop. The result is sent to the flow rate calculation unit 11.

  In the flow rate calculation unit 11, the total time 48 is divided by the number of times of sing-around, and a value obtained by subtracting the delay time 46 from the value is T1 shown in Expression (1).

  Next, using the switching unit 10, the transmission unit 3 is connected to the second ultrasonic transducer 2 with low impedance, and the reception unit 6 is connected to the first ultrasonic transducer 1 with low impedance. Then, ultrasonic waves are generated from the second ultrasonic transducer 2 by the same procedure as described above, and the first ultrasonic transducer 1 receives the ultrasonic waves. At this time, it is preferable to use the value of the first ultrasonic transducer 1 as the resonance frequency used to determine the timing for generating the second drive signal. However, when the difference between the resonance frequencies of the two ultrasonic transducers is small, the resonance frequency of the second ultrasonic transducer may be used.

  After repeating the transmission / reception loop a predetermined number of times, the timing unit 9 counts the total time 48 required to repeat the loop and sends the measurement result to the flow rate calculation unit 11. A value obtained by dividing the total time 48 by the number of times of sing-around and subtracting the delay time 46 from the value is T2 shown in Expression (1).

  By substituting the values of T1 and T2 and the angle θ into the equation (2), the flow velocity V of the fluid is obtained. Further, if the cross-sectional area of the flow path 12 is S, the flow rate Q can be obtained by V × S. The flow rate Q is an amount by which the flow rate moves per unit time, and the amount of fluid can be obtained by integrating the flow rate Q.

  As described above, according to the present embodiment, even when the reception ultrasonic transducer resonates due to the leakage of the drive signal generated in the switching unit, the leakage is actively used to control the phase of the resonance vibration. Measurement errors in flow measurement can be reduced.

  As is clear from the above description, the influence of the resonance vibration of the receiving ultrasonic transducer can be reduced by receiving the ultrasonic wave a plurality of times while changing the phase of the resonance vibration. The method of receiving the ultrasonic waves is not limited to the single-around method. For example, in each measurement, the transmission time and the reception (detection) time of the ultrasonic wave may be measured to obtain the propagation time, and the propagation time in one direction may be obtained using the total value.

  Further, in the present embodiment, the case where the ultrasonic transducer resonates due to the leakage of the drive signal generated by the switching unit has been described, but the present invention also applies to the case where the receiving ultrasonic transducer resonates due to other causes. The influence of resonance can be effectively reduced. For example, the reception ultrasonic transducer vibrates by receiving the ultrasonic wave transmitted from the transmission ultrasonic transducer, but the reception ultrasonic transducer continues to vibrate at the resonance frequency even after the vibration is attenuated. There is a case. Even in such a case, as described above, the influence of resonance can be reduced by causing the receiving ultrasonic transducer to resonate at a predetermined phase.

(Second Embodiment)
FIG. 9 is a block diagram showing a second embodiment of the ultrasonic flowmeter according to the present invention. The ultrasonic flowmeter 102 is different from the first embodiment in that it includes a transmission unit 56 instead of the transmission unit 51 of the first embodiment.

  In the first embodiment, in order to drive the reception ultrasonic transducer, the reception ultrasonic transducer is driven by using the signal leakage in the switching unit 10, but in the present embodiment, the transmission unit And a receiving ultrasonic transducer are connected with a low impedance to give a drive signal. For this purpose, the transmission unit 51 includes a first drive signal generation unit 57, a second drive signal generation unit 38, a delay unit 39, and a switch unit 43.

  The first drive signal generation unit 57 is connected between the control unit 54 and the switching unit 10. When a trigger signal is output from the control unit 54, the first drive signal generation unit 57 generates a first drive signal based on the trigger signal and outputs the first drive signal to the switching unit.

  The second drive signal generation unit 38 and the delay unit 39 are connected in series, and are connected between the control unit 54 and the switching unit 10. When the trigger signal is output from the control unit 54, the delay unit 39 outputs a signal to the second drive signal generation unit 38 and the delay unit 39 after a predetermined delay time has elapsed after receiving the trigger signal. The second drive signal generation unit 38 generates a second drive signal based on the signal received from the delay unit 39 and outputs the second drive signal to the switching unit.

  The switch unit 43 is connected between the switching unit 10 and the receiving unit 6 and includes, for example, a switch control unit 40 and a switch 41. The switch unit 43 receives a signal from the delay unit 39 and electrically disconnects the switching unit 10 and the receiving unit 6 for a predetermined period.

  Therefore, when the ultrasonic wave is transmitted from the first ultrasonic transducer 1 to the second ultrasonic transducer 2 and the propagation time of the ultrasonic wave propagating in the fluid is obtained, the switching unit 10 transmits the ultrasonic wave. The first ultrasonic transducer 1 that is a trusted ultrasonic transducer and the first drive signal generator 57 are electrically connected with low impedance. In addition, the second ultrasonic transducer 2, which is a receiving ultrasonic transducer, and the second drive signal generation unit 38 and the switch unit 41 are electrically connected with low impedance.

  The signals output from the first drive signal generation unit 57 and the second drive signal generation unit 38 have appropriate amplitudes for driving the transmission ultrasonic transducer and the reception ultrasonic transducer, respectively. It is so amplified. The second drive signal output from the second drive signal generation unit 38 only needs to have an amplitude enough to cause the receiving ultrasonic transducer to resonate and receive ultrasonic waves propagating in the fluid. The amplitude is sufficiently smaller than the amplitude of the first drive signal so as not to adversely affect the operation.

  The operation of the ultrasonic flowmeter 102 will be described with reference to FIG. FIG. 10 shows the output signals of the first drive signal generation unit 57 and the second drive signal generation unit 38 and the vibration amplitudes of the transmission ultrasonic transducer and the reception ultrasonic transducer along the time axis. Yes.

  As shown in the figure, when the first drive signal 61 is output from the first drive signal generator 57 at time t1, the transmission ultrasonic transducer has a waveform at substantially the same time by the first drive signal 61. It begins to vibrate at 61a. At the same time, the first drive signal is also output to the reception ultrasonic transducer by capacitive coupling in the switching unit 10. Therefore, the receiving ultrasonic transducer starts to vibrate with the waveform 61b. When the output of the first drive signal 61 ends, the receiving ultrasonic transducer continues to vibrate with the waveform 63.

  When the second drive signal 62 is output from the second drive signal generation unit 38 at time t2, the switching unit 10 causes the second ultrasonic transducer 2 that is a reception ultrasonic transducer and the second drive signal to be output. Since the generator 38 is connected with a low impedance, the receiving ultrasonic transducer receives the second drive signal and starts to vibrate with the waveform 62a ′. Thereafter, when the output of the second drive signal 62 is completed, the vibrations of the transmission ultrasonic transducer and the reception ultrasonic transducer are attenuated. Similarly, the reception ultrasonic transducer is at the resonance frequency indicated by the waveform 64 ′. Continue to vibrate. The phase of the resonance vibration indicated by the waveform 64 ′ is determined at the output time t 2 of the second drive signal 62.

  At this time, the switching unit 10 and the receiving unit 6 are electrically disconnected by the switch unit 43. For this reason, the second drive signal is not output to the receiving unit 6, and the second drive signal is not detected.

  Thereafter, the ultrasonic wave generated by the first drive signal 61 propagates through the fluid from the transmitting ultrasonic transducer and reaches the receiving ultrasonic transducer. At this time, the receiving ultrasonic transducer vibrating at the resonance frequency indicated by the waveform 64 vibrates as indicated by the waveform 61c by the received ultrasonic wave. That is, the vibration due to reception is superimposed on the resonance vibration. As described in the first embodiment, the time when the receiving ultrasonic transducer starts to vibrate by the ultrasonic wave propagating in the fluid is after the time t3 from the time t1, and this time is the time when the ultrasonic wave is in the fluid. Is equal to the propagation time to propagate. This time is constant. On the other hand, the phase in the case where the receiving ultrasonic transducer performs the resonance vibration indicated by the waveform 64 is determined at the timing when the second drive signal is generated. For this reason, similarly to the first embodiment, by repeatedly performing measurement by sing around while changing the phase of the resonance vibration waveform 64 ′, it is possible to cancel the influence of the resonance vibration.

  According to this embodiment, the receiving ultrasonic transducer is driven directly instead of as a leakage signal. For this reason, it is easy to control the signal for driving the reception ultrasonic transducer, the resonance vibration of the reception ultrasonic transducer can be controlled more accurately, and the influence of the resonance vibration can be reduced.

(Third embodiment)
Hereinafter, the gas meter provided with the ultrasonic flowmeter of the present invention will be described.

  FIG. 11 shows a block diagram of the gas meter 103 for measuring the flow rate of the gas flowing in the pipe 70. The gas flowing in the pipe 70 may be other gases such as hydrogen and oxygen, in addition to those used in general households such as natural gas and propane gas.

  The gas meter 103 controls the ultrasonic flow meter 71 for measuring the flow rate of the gas flowing in the pipe 70, the cutoff valve 72 for shutting off the gas flowing in the pipe 70 in an emergency, the ultrasonic flow meter 71 and the cutoff valve 72. A signal processing device 73 such as a microcomputer, and a display unit 74 that displays a flow rate measured by using an ultrasonic flowmeter 71, an integrated value of the flow rate, and other information.

  As the ultrasonic flow meter 71 of the present embodiment, the ultrasonic flow meter of the first or second embodiment is used.

  Data relating to the flow rate measured by the ultrasonic flowmeter 71 is processed by the signal processing device 73 and displayed on the display unit 74. Further, the signal processing device 73 monitors whether there is an abnormality in the flow rate to be measured. For example, when a large flow of gas suddenly begins to flow or when a low flow of gas flows for a long time, it is determined that a gas leak has occurred, and the shutoff valve 72 is operated to supply the gas. To stop.

  The gas meter 103 transmits data relating to the measured flow rate and information relating to gas leakage to a gas company or the like, and includes a communication unit 75 for remotely operating the signal processing device 73 for maintenance from the gas company. Good. Alternatively, another interface for communicating with a home security system or the like may be provided.

  According to the gas meter of the present embodiment, it is possible to accurately measure the flow rate even when the gas flow rate is small. For this reason, even when a small amount of gas leakage occurs, it is possible to correctly detect the flow rate and issue a gas leakage warning.

  The present invention can be used for a flow meter and a gas meter for measuring the flow rates of various gases including natural gas and propane gas. In particular, it is possible to accurately measure the flow rate or flow rate of a gas with a low flow rate, and it can also be used to measure a fluid with a large flow rate change.

It is a block diagram which shows 1st Embodiment of the ultrasonic flowmeter of this invention. It is a figure explaining the vibration state of the ultrasonic transducer for reception of the ultrasonic flowmeter shown in FIG. It is a figure explaining the timing of the drive signal output from a transmission part. It is a figure which shows the timing of the drive signal which leaks in a switching part and is input into the ultrasonic transducer | vibrator for reception. It is a figure which shows the time change of the vibration state of the ultrasonic transducer | vibrator for reception. It is another figure which shows the time change of the vibration state of the ultrasonic transducer | vibrator for reception. (A) And (b) is a graph which shows that a signal attenuate | damps by superimposing the signal from which a phase differs. It is a figure explaining the measurement by a sing-around method. It is a block diagram which shows 2nd Embodiment of the ultrasonic flowmeter of this invention. It is a figure explaining the vibration state of the ultrasonic transducer for reception of the ultrasonic flowmeter shown in FIG. It is a block diagram which shows the structure of the gas meter by this invention. It is a block diagram which shows the conventional ultrasonic flowmeter. It is a figure which shows the cross section of the flow path in which the ultrasonic flowmeter shown in FIG. 12 was installed. It is a figure explaining zero cross detection. It is a figure explaining the leak to the ultrasonic transducer for reception of a drive signal. It is a figure which shows the vibration state of the ultrasonic transducer for transmission and reception. It is a figure explaining that an error arises in detection of a received signal by resonance vibration of an ultrasonic transducer for reception.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st ultrasonic transducer 2 2nd ultrasonic transducer 3 Transmission part 4, 22, 39 Delay part 5 Level detection part 6 Reception part 7 Zero cross detection part 8 Repetition part 9 Time measurement part 10 Switching part 11 Flow volume calculation part 12 channel 13 peak hold unit 20 first waveform generation unit 21 second waveform generation unit 38 second drive signal generation unit 51, 56 transmission unit 52 amplification unit 53 detection unit 54 control unit 55 calculation unit 57 first Drive signal generation unit 43 Switch unit 71, 101, 102 Ultrasonic flow meter 72 Shut-off valve 73 Signal processing device 74 Display unit 103 Gas meter

Claims (27)

An ultrasonic flowmeter that performs transmission and reception of ultrasonic waves and measures a flow rate at which a fluid moves through a flow path based on a two-way propagation time difference of the ultrasonic waves,
A pair of ultrasonic transducers each functioning as an ultrasonic transmitter and receiver and arranged to form a propagation path of the ultrasonic wave in a fluid flow path;
A transmitting unit that drives a transmitting ultrasonic transducer functioning as the transmitter of the pair of ultrasonic transducers;
A receiving unit that adjusts the amplitude of the received signal by the ultrasonic wave received by the receiving ultrasonic vibrator functioning as the receiver among the pair of ultrasonic vibrators;
With
The ultrasonic flowmeter, wherein the transmission unit drives the reception ultrasonic transducer at a timing different from a timing at which the transmission ultrasonic transducer is driven in order to measure a flow rate.   The ultrasonic flowmeter according to claim 1, wherein the transmission unit drives the ultrasonic transducer for reception so as to reduce an influence due to resonance vibration of the ultrasonic transducer for reception.   The ultrasonic flowmeter according to claim 2, wherein the propagation time of the ultrasonic wave in one direction is obtained by transmitting the ultrasonic wave a plurality of times at different timings for driving the ultrasonic transducer for reception. A pair of ultrasonic transducers each functioning as an ultrasonic transmitter and receiver and arranged to form a propagation path of the ultrasonic wave in a fluid flow path;
Of the pair of ultrasonic transducers, a first drive signal for driving a transmission ultrasonic transducer functioning as the transmitter at a first timing and the receiver of the pair of ultrasonic transducers. A transmitter for outputting a second drive signal for driving the functioning ultrasonic transducer for reception at a second timing;
A receiver that adjusts the amplitude of the received signal by the ultrasonic wave received by the receiving ultrasonic transducer;
The transmitting unit is connected to one of the pair of ultrasonic transducers and the receiving unit is connected to the other of the pair of ultrasonic transducers so that ultrasonic waves can be transmitted and received bidirectionally between the pair of ultrasonic transducers. A switching unit for connecting
A detection unit for detecting the received signal;
An ultrasonic flowmeter that obtains the flow rate of the fluid from the propagation time difference in both directions by obtaining a propagation time during which the ultrasonic wave propagates through a propagation path based on detection of the received signal.   In order to measure the flow rate of the fluid by repeating transmission and reception of the ultrasonic wave by a sing-around method, a detection signal indicating that a reception signal has been detected is received from the detection unit, and after a predetermined time has passed, The ultrasonic flowmeter according to claim 4, further comprising a controller that outputs a trigger signal for outputting the first and second drive signals.   The ultrasonic flowmeter according to claim 5, wherein the first timing is constant and the second timing is changed in repetition by the sing-around method.   The ultrasonic flowmeter according to claim 4, wherein the second timing is determined based on a resonance frequency of the ultrasonic transducer.   The ultrasonic flowmeter according to claim 7, wherein the second timing changes periodically in repetition by the sing-around method.   The ultrasonic flowmeter according to claim 8, wherein the number of repetitions by the sing-around method is an integral multiple of the number of times the periodic change of the second timing occurs.   The second timing is determined so that the second drive signal is output before the reception ultrasonic transducer receives the ultrasonic wave transmitted by the first drive signal. The ultrasonic flowmeter described in 1.   The driving of the reception ultrasonic transducer by the transmission unit is such that the second drive signal is received from the transmission unit by the high impedance connection between the reception ultrasonic transducer and the transmission unit in the switching unit. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is output by being output to an ultrasonic transducer for use.   The transmission unit receives the trigger signal and generates the first drive signal, a first waveform generation unit, a delay unit that receives the trigger signal and outputs a signal after a predetermined time, and the delay A second waveform generation unit that receives the signal from a unit and generates the second drive signal, and a signal amplification unit that amplifies the first drive signal and the second drive signal. 11. The ultrasonic flowmeter according to 11.   The driving of the reception ultrasonic transducer by the transmission unit is such that the second driving signal is received from the transmission unit by the low impedance connection between the receiver ultrasonic transducer and the transmission unit in the switching unit. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is output by being output to an ultrasonic transducer for use. The transmitter is
A first drive signal generation unit that is inserted between the control unit and the switching unit, receives the trigger signal, and generates the first drive signal;
A delay unit that receives the trigger signal and outputs the signal after a predetermined time;
Receiving the signal from the delay unit, generating the second drive signal, and outputting the second drive signal to the switching unit;
A switch unit that cuts off an electrical connection between the switching unit and the receiving unit while the second drive signal is generated from the second drive signal generation unit;
The ultrasonic flow meter according to claim 13.   A gas meter comprising the ultrasonic flowmeter defined in any one of claims 1 to 14. A pair of ultrasonic transducers each functioning as an ultrasonic transmitter and receiver are arranged so that an ultrasonic propagation path is formed in the fluid flow path, and both of the ultrasonic waves propagating through the propagation path are arranged. An ultrasonic flow measurement method that measures the flow rate of a fluid based on a propagation time difference in a direction,
A flow rate measurement method for driving at a timing different from a timing for driving a transmitting ultrasonic transducer using a receiving ultrasonic transducer functioning as a receiver as the transmitter.   The flow rate measurement method according to claim 16, wherein the reception ultrasonic transducer is driven so as to reduce an influence of resonance vibration of the reception ultrasonic transducer.   The flow rate measurement method according to claim 17, wherein the propagation time of the ultrasonic wave in one direction is obtained by transmitting the ultrasonic wave a plurality of times at different timings for driving the reception ultrasonic transducer.   The flow rate measurement method according to claim 18, wherein the ultrasonic wave propagation time is obtained from a total time required for repeating the ultrasonic wave transmission / reception a plurality of times by a sing-around method. Outputting a first drive signal for driving the ultrasonic transducer for transmission at a first timing and a second drive signal for driving the ultrasonic transducer for reception at a second timing;
The flow rate measurement method according to claim 19, wherein the first timing is made constant and the second timing is changed in repetition by the sing-around method.   The flow rate measurement method according to claim 20, wherein the second timing is determined based on a resonance frequency of the ultrasonic transducer.   The flow rate measuring method according to claim 21, wherein the second timing is periodically changed in repetition by the sing-around method.   23. The flow rate measurement method according to claim 22, wherein the number of repetitions by the sing-around method is set to an integer multiple of the number of times the periodic change of the second timing occurs.   The flow rate measurement according to claim 23, wherein the second timing is determined so that the second signal is output before the reception ultrasonic transducer receives the ultrasonic wave transmitted by the first signal. Method. The reception ultrasonic transducer adjusts the amplitude of a reception signal received by the pair of ultrasonic transducers, a transmission unit that generates the first and second drive signals, and the reception ultrasonic transducer. A switching unit for selectively connecting the receiving unit,
25. Any one of claims 16 to 24, wherein the second signal is output from the transmission unit to the reception ultrasonic transducer by a high impedance connection between the reception ultrasonic transducer and the transmission unit in the switching unit. The flow measurement method according to Crab. The reception ultrasonic transducer adjusts the amplitude of a reception signal received by the pair of ultrasonic transducers, a transmission unit that generates the first and second drive signals, and the reception ultrasonic transducer. A switching unit for selectively connecting the receiving unit,
25. Any one of claims 16 to 24, wherein the second signal is output from the transmission unit to the ultrasonic transducer for receiver by a low impedance connection between the reception ultrasonic transducer and the transmission unit in the switching unit. The flow measurement method according to Crab.   A computer-readable recording medium on which a program for causing a computer to execute the flow rate measuring method defined in any one of claims 16 to 26 is recorded.

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